Taxi Fare for Checker Cab, the official WDW taxi (run by Mears)
$2.20 for the first 1/4 mile and .55 for each additional mile. Official taxi's do not have to pay parking fee which an unofficial taxi does. The driver then will charge it's guests the additional fee if you need to pass through a toll booth.
Now if you choose an unofficial taxi and they have already paid the parking fee, you should not be charged for it. Make sure that you ask this up front.